Association between polymorphisms of DNA repair genes and intracranial aneurysms: A systematic review and meta‑analysis

Intracranial aneurysms (IAs) are present in ~2% of the general population, and genetic factors cannot be excluded for the risk of their development. The gene factors that result in the changes in the vascular extracellular matrix (ECM) may also be a key reason for IAs being hereditary. The VCAN gene [also known as chondroitin sulfate proteoglycan 2 (CSPG2)] plays various roles in maintaining ECM functions. The present systematic review and meta-analysis aimed to investigate all eligible articles involving IAs on the association with germ line SNPs of DNA repair genes (up to January, 2024). The total number of patients was 2,308 [987 cases (poor outcomes) and 1,321 controls (good outcomes)]. The results revealed that rs2287926 G/G genotype and G allele and rs251124 T/T genotype and minor allele T increased the risk of developing IAs. However, further studies are required to examine these gene polymorphisms as screening markers for IAs.


Introduction
Intracranial aneurysms (IAs) can be found in ~2% of the general population and are revealed in 85% of subarachnoid hemorrhage cases (1)(2)(3).More commonly, patients between 40 and 60 years of age are more prone to IA rupture with an unfavorable outcome.It has been found that ~50% of cases succumb and another 20% remain with disability after management (4)(5)(6)(7).
Several investigators have inspected the expansion of IAs, which are usually considered to be caused by the interactivity among environmental and hereditary causes (8)(9)(10).For example, environmental factors, such as alcohol consumption, smoking and hypertension are suggested to be common risk factors for IAs (8)(9)(10).On the other hand, hereditary causes cannot be eliminated as a risk factor for IAs.Hereditary susceptibility is the main risk parameter for the formation of IA, with an up to seven-fold increased risk of rupture (11).Another study also stated a five-fold increased risk of IA rupture in a first-degree individual among families with a prevalence of IAs (12).Furthermore, genes cause alterations in the vascular extracellular matrix (ECM), which may also be a significant cause for IAs to be hereditary entities (13,14).ECM modification (disruption or remodeling) plays a crucial role in preserving the composition and integrity of the arterial wall.ECM degradation is a key characteristic of IAs (13,14).
The Versican (VCAN) gene [also known as chondroitin sulfate proteoglycan 2 (CSPG2)] has multiple functions in preserving ECM roles (13,14).Previous research has indicated that the three single nucleotide polymorphisms (SNPs), rs2287926, rs173686 and rs251124 of the VCAN gene, are related to the development of IAs (3,13,14).Nevertheless, replication research has stated a lack of an association among the CSPG2 variants (rs251124 and rs173686) and the presence of aneurysms (15,16).
The purpose of the present meta-analysis was to evaluate the involvement of the VCAN gene variants in the development of IAs and its importance as a screening global marker for the pathogenesis of IAs.The findings presented herein may help clinicians identify the exact risk of their development.

Study identification and selection.
To investigate all eligible articles involving IAs in the literature written in the English language on the association with germ-line SNPs of DNA repair genes and IAs through electronic databases, including the Cochrane Library, PubMed (up to January, 2024), Embase (up to January, 2024) and MEDLINE (up to January, 2024) via combinations of the following terms: Intracranial aneurysms; aneurysms; gene associations; SNPs; CSPG2 gene.For the study protocol creation and design, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were applied.The flowchart with the collec-

Association between polymorphisms of DNA repair genes and intracranial aneurysms: A systematic review and meta-analysis
tion process of the enclosed articles is illustrated in Fig. 1.The present study integrated articles published between 1980 and 2023.
The subsequent information was inserted from the article pool: The authors' names and year of publication, the sample of total cases and controls, the mean age and sex of cases and controls, the DNA polymorphisms and DNA repair genes inspected in the study, genotyping techniques, the polymorphism's genotype, the number of cases and controls, the chromosome position, and the possible mechanisms of function were considered qualified.For the CSPG2 rs188703, rs2287926, rs251124 and rs173686 SNPs, meta-analyses were carried out (Table I).Of note, data from genome-wide association studies were not included in any phases, but only data from candidate gene association studies were included.All genetic models (dominant, recessive and additive) were evaluated in studies recording genotype frequencies.The alleles and the SNP IDs are presented in Table I.

Statistical analysis and assessment of heterogeneity.
All analyses were performed using Review Manager Software (RevMan), version 5.4 (https://training.cochrane.org/onlinelearning/coresoftware/revman).A fixed-and random-effects model meta-analysis was used [according to the Cochrane Handbook for Systematic Reviews of Interventions (version 5.1.0)(17)] for the evaluation of the proportion estimate for every outcome independently, as the I 2 statistic calculated the heterogeneity.A value of I2 in an amount <50% was considered as low heterogeneity, and a value >50% as high heterogeneity.Or else, the fixed-effect model was performed.The continuous outcomes were stated as a weighted mean difference with 95% confidence intervals (CIs).For discontinuous variables, odds ratios (ORs) with 95% CIs were used for the evaluation.A P-value <0.05 was considered to indicate a statistically significant difference.
Epidemiological and clinical features.The authors, publication year, genes, SNP ID, mean age of the patients, and sample of males and females between the cases and controls among the studies are presented in Table II.

CSPG2-rs188703. Information regarding the SNP rs188703
was available in two articles (15,18) and demonstrated no statistically significant difference between the patients with IAs (cases with poor outcomes) and the controls (OR, 1.08; 95% CI, 0.86-1.35;P= 0.51) (Fig. 2A and Table ΙΙΙ).SNP rs188703 was found in 305 of 900 (33.8%) control patients and in 200 of 579 (34.5%) cases.When investigating the funnel plot, it was established that there was no heterogeneity (P=0.70 and I 2 =0%) and no publication bias (Fig. 2B).

Discussion
There are different hypotheses about the formation of aneurysms, most of which involve inappropriate ECM modification (19).The VCAN gene plays several roles in preserving ECM processes (13,14).It has been shown that individuals with the rs251124 polymorphism T allele are at an increased risk of developing IAs, and the CT genotype has been found to be distinct as a risk factor for the incidence of aneurysms in a southern Indian population (20).Overall, there has been an association between the development of IAs in the European population and the rs173686 polymorphism (19).Specifically, it has been shown that the rs173686 G/G genotype and G allele are associated with an increased risk of IA formation (13,19).The present meta-analysis investigated the associations among four SNPs in the VCAN gene polymorphism and IA susceptibility.The results revealed that the rs2287926 G/G genotype and G allele, and rs251124 T/T genotype and minor T allele increased the risk of developing IAs.No significant differences in allele or genotype frequencies among the control and case groups were noted with the rs188703 and rs173686 SNPs.Additional results revealed the VCAN gene to be involved in the development of IAs.
identified the minor T allele of the rs251124 T/T genotype and the rs2287926 G/G genotype and G allele.
In the literature, researchers have verified the association between VCAN (CSPG2) genes and the risk of developing IAs (13,14).On the contrary, according to certain studies, there is no confirmed association between the CSPG2 variants (rs173686 and rs251124 polymorphisms) and IA susceptibility (3,16,19).These studies report that geographical and racial reasons may affect the aforementioned conflicting results.However, the heterogeneity of the population and the small number of cases may be the reasons for these different results compared with the present meta-analysis.
In addition, similar to the results of previous studies, members of the same ethnic group also have diverse susceptibilities (3,14,15).Sun et al (16) reported that the two rs25112 and four rs173686 SNPs of the CSPG2 gene were not associated with IAs in the Northern Chinese (Beijing) Han population.It is known that the incidence of IAs may be the consequence of complex results from both hereditary and environmental aspects.The primary explanation for this discrepancy may be topographical variations (19).Other environmental reasons, including sex, cigarettes and alcohol consumption, hypertension and hormonal profiles have been proposed to be associated with the development of IAs (9,10,21,22).On the other hand, ECM-related genes can also undergo alterations from various environmental factors, such as radiation, provoking a remodeling or disruption of the ECM of the arterial wall (13).
The present study had certain limitations which should be mentioned.The present meta-analysis pool was performed from proportionately small samples; consequently, the results require authentication from a large-scale participant.Another limitation was the heterogeneity between populations.It has been hypothesized that hereditary heterogeneity between different populations can lead to paradoxical results.In addition, the majority of enrolled articles included patients with ruptured and unruptured IAs; thus, aneurysm rapture may not be associated with SNP variation.
In conclusion, the present meta-analysis revealed that rs2287926 G/G genotype and minor allele G, rs251124 T/T genotype and minor T allele were associated with an increased risk of developing IAs.The results presented herein suggest that the VCA N (CSPG2) gene is an IA-predisposed gene and merits further investigation as a screening global marker for IAs.Thus, VCAN is a key candidate gene involved in the pathogenesis of IAs.This may help clinicians indentify the exact risk factors associated with the development of IAs.Future studies are required however, to examine these gene polymorphisms as screening markers for IAs.

Figure 1 .
Figure 1.Flowchart of the study selection process.

Figure 3 .
Figure 3. (A) Forest plot for CSPG2-rs2287926.The results demonstrate a statistically significant difference between patients with intracranial aneurysms (cases with poor outcomes) and the controls (OR, 1.37; 95% CI, 0.99-1.91;P=0.0500), and with low heterogeneity (P=0.18 and I 2 =45%).(B) Funnel plots of the CSPG2-rs2287926 with low heterogeneity (P=0.18 and I 2 =45%) and thus, low publication bias.CSPG2, chondroitin sulfate proteoglycan 2; I 2 , the percentage of total variation across studies that is due to heterogeneity rather than chance; CI, confidence interval; P, P-value; OR, odds ratio.

Figure 4 .
Figure 4. (A) Forest plot for CSPG2-rs251124.The results demonstrate a statistically significant difference between patients with intracranial aneurysms (cases with poor outcomes) and the controls (OR, 1.34; 95% CI, 1.05-1.70;and P=0.02), and with no heterogeneity (P=0.48 and I 2 =0%).(B) Funnel plots of the CSPG2-rs251124 with no heterogeneity (P=0.48 and I 2 =0%) and thus, no publication bias.CSPG2, chondroitin sulfate proteoglycan 2; I 2 , the percentage of total variation across studies that is due to heterogeneity rather than chance; CI, confidence interval; P, P-value; OR, odds ratio.

Table I .
Gene, chromosome position, possible mechanisms of function, and number of studies included in the present metaanalysis.